Oriented films may be formed from the molten polymer by a number of methods known in the art (for example, cast film extrusion or blown film extrusion). Films can be oriented in one direction by hot-drawing in the machine direction with a tensioning device, and annealing. Films can also be oriented in two directions (machine direction and transverse direction) by suitable tensioning devices. Oriented polyamide films are useful for a wide variety of packaging applications.
Tapes may be prepared from extruded films. Flat films can be extruded into a cooling water bath or onto chilled rolls for quenching. Alternatively, a tubular blown film can be extruded through an annular die and air-quenched. The quenched film is then knife-slit into tapes. The tapes are then stretched (i.e. uniaxially oriented) to several times their original length by hot-drawing in the machine direction with a tensioning device and annealing the stretched tapes having controlled widths (for example from about 1 cm to about 5 cm). Polyamide tapes can be used in a number of applications. For example, tapes can be coated with a variety of appropriate adhesives to prepare adhesive tapes.
Fibers may be formed directly from the molten polymer by a number of methods known in the art, including melt-spinning, centrifugal spinning and melt-blowing.
Melt-spun or melt-blown fibers can be used in nonwoven textiles suitable for applications such as carpet backing, agrotextiles and geotextiles.
Polyamide fibers can be used in twines or ropes or to prepare yarns for carpets. Polyamide yarns also can be woven or knitted into fabrics used in applications such as tarpaulins, liners, banners, sacking, carpet backing, agrotextiles and geotextiles.
It is desirable to provide oriented polyamide films, tapes and fibers with improved mechanical properties such as tensile breaking load, tenacity (tensile breaking stress) and elongation at break. To reduce the cost of stretched slit-film tapes it is desirable to reduce the denier (similar width but lower thickness) of the tape and/or increase the amount of inert filler such as CaCO3 in the polyamide formulation. Polyamide fibers with improved mechanical properties have been prepared by adding small amounts of additives to polyester. See, e.g., EP 80274B1, EP 35796B1, EP 41327B1 and JP 56-85420.
With known polyamide compositions, however, it is difficult to achieve the desired improvements. Higher stretch ratios and reduced denier can result in unacceptable loss of physical properties. Undesirable fibrillation of polyamide tapes under high stretch ratios is desirably overcome.
It also remains desirable to enhance the draw efficiency and the flex fatigue resistance of oriented films, tapes, and fibers with low deniers or thicknesses.